How are my AFR's
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How are my AFR's
Trying to get this carb thing down. This is a pull in first gear from 4krpm to the limiter at 7K. LM7, TH350 with 4000 converter, 4.11 gears, Holley 750 mech secondary's. Just seeing where the AFR's should bee across the powerband. This is an N/A pull, I have a dedicated fuel cell for the nitrous.
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#2
I slowed the video down a bit, you can see it starts creeping up towards 14 as the rpms go up. Unsure how reliable a first gear pull is though. I think people usually do a 3rd gear pull when tuning WOT.
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It definitely creeps up. I would not want it to move much, it should stay fairly consistent ideally. The richest spot is usually peak torque in a fuel injected application but that is not possible to control with a carb, so a nice full run where the number just sits on say, 13.4, is ideal as a baseline for a carb at WOT.
The actual perfect A/F depends on hundreds of other factors. Some engine will tolerate 14's at wot, some will demand 12's. Some run well at 10:1 and others don't even want to go near 10:1.
iirc the general guideline for N/A medium compression engine would be around 13.5~ maybe 13.2 is "safest". I would use 12.8:1 with up to about 5psi of boost on a 9:1 random engine personally, so surely 12.8 is too rich for the majority of medium compression (typical pump gas ratios nothing crazy) NA builds. You are using nitrous so you might want it slightly richer from the get-go however. It depends how the fuel side of the nitrous system is setup since if you are using C16 in that spare fuel cell then you probably won't want the engine richer off the nitrous than normal.
The actual perfect A/F depends on hundreds of other factors. Some engine will tolerate 14's at wot, some will demand 12's. Some run well at 10:1 and others don't even want to go near 10:1.
iirc the general guideline for N/A medium compression engine would be around 13.5~ maybe 13.2 is "safest". I would use 12.8:1 with up to about 5psi of boost on a 9:1 random engine personally, so surely 12.8 is too rich for the majority of medium compression (typical pump gas ratios nothing crazy) NA builds. You are using nitrous so you might want it slightly richer from the get-go however. It depends how the fuel side of the nitrous system is setup since if you are using C16 in that spare fuel cell then you probably won't want the engine richer off the nitrous than normal.
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I got a logger to make it easier to see/watch/replay
But, this is the general agreed AFR........
Attachment 681460
My AFR at 7000 was 12.7 and 12.3 at 7500
But, this is the general agreed AFR........
Attachment 681460
My AFR at 7000 was 12.7 and 12.3 at 7500
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I slowed the video down a bit, you can see it starts creeping up towards 14 as the rpms go up. Unsure how reliable a first gear pull is though. I think people usually do a 3rd gear pull when tuning WOT.
https://youtu.be/QDWV13M49vI
https://youtu.be/QDWV13M49vI
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So, I think you could be losing vacuum and the power valve closing cheating you out of the extra fuel.
Some even run no PV, but when you do this, you need to jet up about 8 sizes.(I would not do on a street vehicle)
Last edited by Doug G; 08-14-2017 at 05:49 PM.
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Power Valve too high (low number) and loosing that added fuel ?
So, I think you could be losing vacuum and the power valve closing cheating you out of the extra fuel.
Some even run no PV, but when you do this, you need to jet up about 8 sizes.(I would not do on a street vehicle)
So, I think you could be losing vacuum and the power valve closing cheating you out of the extra fuel.
Some even run no PV, but when you do this, you need to jet up about 8 sizes.(I would not do on a street vehicle)
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